Delta Grounding System

Hi

any body has experience also about triad ground rod assembly method (delta grounding rod installation), with 10 ft min. standard between the third ground rods, and connected each others with bare copper 4/0 AWG. This is become the standard of grounding plan for building since 1978 till now at my engineering office where I am working, may be you can explain the advantage and disadvantage between the other methods

thanks

1250 Hp 3ph 3.3kv Ind. Motor Protection

Hi All,
This is my first time join with LMP Forum.

at this moment, I`m preparing the design stuff of air compressor 1250HP 3.3kV 50Hz to be constructed in our utility. During the purchasing preparation by another guys before, i wasn`t involved especially for the motor specifications etc, then its gone to be purchased and on the way. I am the second man continue this project.

ones in our spec. about motors 1000HP and above, all six stator leads shall be brought out to the terminal box, with three BYZ current transformers connected for differential protection. as far as i knew and my experience, yes it is for a large ind. motor. but the problems the vendor not provide what i am expecting, only 3 stator leads. Many times i confirm about this to the supplier (vendor) but what I got, the extremely low response.

IEEE recommends differential protection for all motors >1000HP and larger on ungrounded/grounded system,
and I thought the motor specialist manufacturer have knwon about this, and the previous guys prepare the spec before I handle this project knew also and should be.

I have 2 Multilin SR469 motor protection relay to be apllied on 2 unit I-R air compressor, and after knowing that I can`t apply one of the function, the diff. prot. relay, given me another things, and just apply the other functions of my SR469.

I`ve calculated and considering that the available short circuit current of system is close to the value of locked rotor current, and the other things of the reasons for me to apply diff. prot. function.

Is there any guys have experiences can share about this ? I need any comments of you as my reference also. and specially for the regulated standard about diff. protection, yes or not, to be applied on >1000HP induction motor

Regards